renal transport mechanism ( dr. hardian )

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RENAL TRANSPORT MECHANISMNaCL AND WATER REABSORPTION ALONG THE NEPHRON

OBJECTIVE

1.Explain the three processes involved in the production of urine a. filtration b. reabsorption c. secretion..2.Describe the magnitude of the processes of filtration and reab- sorption by the nephron.3.Describe the composition of normal urine.4.explain the basic transport mechanisms present in each nephron segment.5.Describe how water reabsorption is “coupled” to Na+ reabsorp tion in the proximal tubule.6.Explain how solutes, but not water , are reabsorbed by the thick ascending limb of Henle’s loop.

OBJECTIVE - COUNT.

7. Describe how Starling forces regulate solute and water reabsorption across the proximal tubule.8. Explain glomerulotubular balance and its phy- siological significance .9. Identify the major hormones that regulate NaCl and water reabsorption by its nephron segment

COMPOSITION OF URINE

SUBSTANCE CONCENTRATION

Na+ 50 - 150 meq/l K+ 20 - 70 meq/l NH4- 30 - 50 meq/l Ca++ 5 - 12 meq/l Mg++ 2 - 18 meq/l Cl - 50 - 130 meq/l PO4 20 - 40 meq/l Urea 200 – 400 mM Kreatinin 6 - 20 mM pH 5 - 7 Osmolality 500 - 800 mOsm/Kg H2O others 0

MECHANISMS OF SOLUTETRANSPORT

PASSIVE . Spontaneous , down an electrochemical gradient no energy requirement. Diffusion Facilitated diffusion ion channel Uniport Coupled transport Antiport Symport

ACTIVE Against an electrochemical gradient, requires direct input of energy Active transport Endocytosis.

Tubuler fluid

Paracellulerpathway

Transcellulerpathway

Tightjunction

Apical cellmembrane

Lateral intercellular space

blood

Na+

K+

Na+

Na+

Basolateralmembrane

CapillaryBasementmembrane

ATP

ATP

ATP

Tubular fluid

blood

Na+

X

Na+H+

HCO3

K+

Na+ATP

X

CO2 + H2O

CA

First half of proximal tubule

Tubular fluid

blood

NaCl

H2O

Na+

Cl-

organics

H2O

0rganics Na+ Cl-

organic Na+ Cl-

organics Na+ Cl-

H2O

Tubular fluid

CL-Na+

Na+ Na+ Na+

H+HbaseBase

Cl-

Cl-Na+

Cl-

H base

K+ATP

K+Cl-

blood

Second half of proximal tubule

Some organic secreted by the proximal tubule

Endogenous anions Drug

cAMP acetazolamideBile salts chlorothiazideHippurate(PAH) furosemideOxalate penicillinProstaglandins probenecidUrate salicylate(aspirin) hidrochlorthiazide bumetanide

Some organic cations secreted by the proximal tubule

Endogenous cations Drugs

Creatinine atropineDopamine isoproterenolEpinephrine cimetidineNorepinephrine morphine quinine amiloride

Tubular fluid

A-

PAHOA-

Na+

K+

Na+

Di/tri carboxylaseDi/tri carboxylase

PAH(OA-)

ATP

BLOOD

HENLE’S LOOP

-Reabsorbs approimately 20 % of filtered Na+, Cl – and K+-Ca+, HCO3- and Mg++-Exclusively in the thick ascending limb-The ascending thin limb and descending thin limb does not reabsorbs.-water is reabsorbed exclusively in the descending thin limb-The ascending limb is impermiable to water

Tubulalar fluid blood

Paracellulardiffusion

Na+2Cl-K+

Na+

K+

H+ CO2 + H2O HCO3

Cl-K+

Na+

K+ATPCA

Na+K+Ca++MG++

H2O

+

DISTAL TUBULE AND COLLECTING DUCT

•Reabsorb approximately 12 % of the filtered Na+ and Cl-•Secrete variable amount of K+ and H+•The first segment: reabsorbs Na+.Cl- and Ca++ and it’s im-•permiable to water.•The last segment of distal tubule and collecting duct: reabsorb ed Na+ and water and secrete K+(princial cell)•Intercalated cell secrete H+ and reabsorb HCO3- and K+

Tubularfluid

blood

Na+

Cl-

H2O

Na+

Cl-K+

ATP

EARLY SEGMENT OFTHE DISTAL TUBULE

Tubularfluid

blood

DISTAL TUBULE AND COLLECTING DUCT

Principal cellNa+

K+

Na+

K+ ATP

Tubularfluid

blood

H+ HCO3

Intercalated cell

CO2 + H2O

CAATP

REGULATION OF NaCL AND WATER REABSORPTION

Tubularfluid

bloodInterstitial space

Basementmembrane

1

3

2

IIcapP cap

P is

II is

1. STARLING FORCES

2. GLOMERULOTUBULAR BALANCE

3. HORMONES

4. SYMPHATIC NERVOUSN SYSTEM

HORMONES that regulate NaCl and water reabsorption

SEGMENT HORMONE EFFECTS

Prox.tubule angiotensin II NaCl H2O glucocorticoids NaCl H2OThick Asc. Aldosteron NaCl limb vasopressin NaCl

Distal Tub./ aldosteron NaCl Collecting Duct atrial natriuretic Pep. NaCl H2O prostaglandin NaCl H2O bradikynin NaCl vasopressin NaCl H2O

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